1. Field of the Invention
The present invention generally relates to the field of wireless computing in mobile ad-hoc networking environments. More specifically, it is directed to the field of Quality-of-Service (QoS) management for adaptive real-time services running on mobile devices, which support different access technologies in dynamic Internet Protocol (IP)based mobile ad-hoc networks where the connectivity of interconnected fixed and/or mobile nodes is unpredictably time-varying. In this connection, the invention presents different methods for a QoS-aware handover procedure based on resource probing, pre-allocating, reserving, and adaptation mechanisms in a typical dynamic mobile ad-hoc scenario. Moreover, the invention proposes an “information dissemination” approach which optimizes prior-art address resolution mechanisms, in particular in a dynamic mobile ad-hoc environment.
2. Discussion of the Background
Mobile ad-hoc networks, which have been the focus of many recent research and development efforts, can be described as temporary multi-hop wireless networks which consist of a number of interconnected mobile nodes such as PDAs, mobile phones or notebooks using a wireless interface to transmit packet data. Such a mobile ad-hoc network is self-organized and does not need any existing network infrastructure or centralized administration. The vision of mobile ad-hoc networking as described in the article Ad hoc Networking (MANET): Routing Protocol Performance Issues and Evaluation Considerations” (RFC 2501, January 1999) by S. Corson and J. Macker is to support robust and efficient operation in mobile wireless networks by incorporating router and host functionality into mobile nodes such that these nodes are able to forward packets on behalf of other mobile nodes and run user applications. Since mobile ad-hoc networks are envisioned to have random, dynamic, sometimes rapidly changing multi-hop topologies, which are composed of relatively bandwidth-constrained wireless links, the introduction of time-sensitive services into the realm of autonomous, mobile, wireless domains will have to face great challenges when considering real-time QoS support.
Typically, mobile ad-hoc networks (MANETs) operate with distributed functions and allow traffic to pass over multiple radio hops between a source and a destination. Routing algorithms and the implications of radio layers are typical features of these networks. The inherent unpredictability in a network whose nodes move poses a challenge to routing and mobility functions if data is consistently transferred between the nodes of the underlying network. Nonetheless, multi-hop radio systems also make it possible to save battery capacity while retaining performance. In any case, the most attractive property of an ad-hoc networking model is perhaps its independence from centralized control and, thus, the increased freedom and flexibility it gives the user.
In order to understand the central idea of the invention, it is necessary to briefly explain some of the most important features involved with currently available QoS-aware handover management technologies according to the state of the art.
As described in the “Element Service Specification Template” (IETF RFC 2216, September 1997) by S. Shenker and S. Wroclawski, different QoS reservation concepts are offered to mobile users today. The term “quality of service” (QoS) thereby refers to the nature of the provided packet delivery service, as described by different parameters such as the currently available bandwidth, packet delay, and packet loss rates. Traditionally, the Internet offers a single-QoS, best-effort delivery, in which the available bandwidth and delay characteristics depend on the instantaneous load. The control over QoS seen by applications is exercised by an adequate provisioning of the underlying network infrastructure. In contrast, a network with dynamically controllable QoS parameters allows individual application sessions to request network packet delivery characteristics according to their perceived needs. Moreover, it may provide different qualities of service to different applications.
For QoS-enabled IP-based networks, there are two main service streams, namely Integrated Services (IntServ) with its accompanying signaling (Resource) Reservation Protocol (RSVP) and “Differentiated Services” (DiffServ) as described in the article “An Architecture for Differentiated Services” (IETF RFC 2475, December 1998) by S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, and W. Weiss. Said differentiated services provide an aggregation of reservations for similar QoS data flows without any signaling. Therefore, DiffServ networks classify packets into one out of a small number of aggregated QoS data flows or “classes”, based on the so-called DiffServ Code Point (DSCP).
The integrated services architecture mentioned above defines a set of extensions to the traditional best-effort (BE) model of the Internet with the object to provide applications with end-to-end QoS. The RSVP as described in the article “Resource Reservation Protocol (RSVP)—Version 1: Functional Specification” (IETF RFC 2205, September 1997) by R. Bradon et al. is an end-to-end control protocol which forms the signaling part of the integrated services architecture. The Internet Architecture Board (IAB) has outlined issues related to these two architectures which can be taken from the article “Next Steps for the IP QoS Architecture” (IETF RFC 2990, November 2000) by G. Huston.
RSVP is a signaling protocol that enables the applications to signal per-flow requirements to the network. Thereby, the reservation is receiver-oriented and the aggregation of said reservations is supported depending on the needs of the respective application. A QoS data flow may have multiple senders, and the protocol supports different reservation styles to dictate how to aggregate reservations for different senders. RSVP performs a simple reservation and maintains a soft-state resource management in the network. Two important message types used by RSVP are “PATH” and “RESV”. Each data source periodically sends a “PATH” message that sets up the path state at the routers along the path from the sender to the receiver. The receiver of each QoS data flow periodically sends a “RESV” message which sets up a reservation state at intermediate routers along the reverse path from the receiver to the sender. Thereby, RSVP assumes a fairly stable path across the network.
The Mobile Resource Reservation Protocol (MRSVP) as described in the article “MRSVP: A Resource Reservation Protocol for an Integrated Services Network with Mobile Hosts” (Department of Computer Science, Technical Report, DCS-TR-337, Rutgers University, USA, July 1997) by A. K. Talukdar, B. R. Badrinath and A. Acharya supports two types of reservations: active and passive reservations: An active reservation corresponds to a QoS data flow over which data is actually exchanged. A passive reservation on the other hand corresponds to a flow in which the resources are reserved along the route, but data is not passing through. This leads to poor network utilization since reserved resources are not used. In this case, the bandwidth of the passive reservations can be used by other QoS data flows that might require weaker QoS guarantees or best-effort services. In general, a mobile host makes an active reservation to its current location and passive reservations to all other locations it might visit. After a successful handover procedure the active and passive reservations are exchanged.
QoS monitoring and adaptation can be understood as an enhancement of pure QoS reservation. INSIGNIA, an IP-based QoS framework as described in the article “INSIGNIA: An IP-based Quality-of-Service Framework for Mobile Ad-hoc Networks” (Journal of Parallel and Distributed Computing, Vol. 60 No. 4, pp. 374-406, April 2000) by Lee et al. is one candidate which supports adaptive services in mobile ad-hoc networks. This framework is based on an in-band signaling and a soft-state resource management approach that is designed to satisfy both mobility and end-to-end QoS requirements in dynamic environments, wherein network topology, node connectivity as well as end-to-end QoS are time-varying. Although INSIGNIA supports fast reservation, restoration, and end-to-end adaptation, it is not yet supported in any existing router implementation. Thereby, INSIGNIA is based on the “break before make” handover principle as it depends on the local routing protocol to reroute the flow traffic to the new access point and then try to restore the flow. In case of failure, the QoS service degrades to the “best-effort” service.
Another issue is the question whether a network state is soft or hard state. RSVP uses the concept of a soft-state resource management. As described in the article “Resource Reservation Protocol (RSVP)—Version 1: Functional Specification” (ETF RFC 2205, September 1997) by R. Bradon et al. and “RSVP: A New Resource ReSerVation Protocol” (IEEE Network, September 1993) by L. Zhang, S. Deering, et al., a soft state exists only as long as periodic messages are sent along the data path. If said messages fail to arrive at some nodes of said network, the soft state is removed. Compared to the soft state, the hard state is applied at the expense of more complicated releasing of resources, especially in the case of failures.
A context transfer protocol is used to transfer the state information of services, e.g. the QoS requirements of real-time applications, during handover from an old to a new access point. This exchange is triggered by so-called “handover indications” received from the data link layer (layer 2). The development of said protocol is part of the work of the IETF Seamoby working group (http://www.ietf org/html.charters/seamoby-charter.html). Within this IETF working group, context transfers are discussed in a wider term, including security information and header compression as well as QoS-related information.
The article “A Framework for QoS Support in Mobile IPv6” (Internet Draft, Internet Engineering Task Force, March 2001) by H. Chaskar et al. discloses a solution to perform QoS signaling along the new network path when a mobile node using Mobile IPv6 acquires a new care-of address. The herein described solution is based on the definition of a new option called “QoS OBJECT OPTION”. This option is included in the hop-by-hop extension header of certain packets, preferably the ones carrying binding messages, propagating between the mobile node and the correspondent node or between the mobile node and regional mobility agent(s). Such an approach takes advantage of mobility signaling inherent in Mobile IPv6 to program QoS forwarding treatment as well along the new network path. It naturally blends in with micro-mobility techniques.
In the proposal “QoS-Aware Handover for Mobile IP: Secondary Home Agent” (Internet draft, April 2000) by A. de Carolis et al., an extension to the Mobile IPv6 (MIPv6) protocol is disclosed that enables a mobile node to perform a so-called QoS-aware handover. It introduces a new mobile agent, the Secondary Home Agent (SHA), which allows the mobile node to establish a new QoS reservation before dropping the old one. The proposal thereby does not specify the method to solicit a Secondary Home Agent every time when the mobile node connects to an access router. Moreover, the proposal requests RSVP support and logical-flow duplication, e.g., PATH/RSVP messages duplication. An important assumption is that the mobile node must be able to activate the wireless link towards the new access router while still keeping the old one. The QoS-aware handover mentioned in the proposal can only be performed when the available QoS on the new link satisfies the current needs of the application. Otherwise, the QoS-aware handover procedure is not performed, and the current connection of the mobile node is maintained.
Besides, several QoS routing solutions are proposed for ad-hoc networks which are based on the data link layer (layer 2). These solutions do not only focus on finding a route from a source to a destination that satisfies the end-to-end QoS requirements but also on achieving the global efficiency in resource utilization. QoS requirements of QoS routing protocols are normally given in terms of certain constant bandwidth or delay.
Research and development efforts concerning iMAQ—an Integrated Mobile Ad-hoc QoS Framework—are based on building a cross-layer architecture to support the access and transmission of multimedia data via a MANET. Thereby, iMAQ is focused on the following aspects:                location management, providing location information of the mobile nodes,        location-based QoS routing, computing routing path and forwarding data packets,        small group communication, building an overlaying multicast tree for a group of mobile users,        adaptive transport layer, providing router-assisted explicit adaptation for end systems,        configuration management, distributing component-based application layer data processing, and        data accessibility service, which includes advertising and replicating data to improve data accessibility.        
The architecture involves cooperation between different layers at each mobile node to support multimedia traffic and adapt to changes in the dynamic mobile ad-hoc environment.
In this connection, it should be noted that the location-based QoS routing mechanism mentioned in this architecture is a measurement-based QoS-aware mechanism. The QoS of the data connection is maintained by monitoring the resource availability of the nodes in the network through location-resource updates. Thereby, only nodes with sufficient resources to support the data connection are used. Said mechanism predicts route breakage and predictively re-computes new routes before the existing connection over the old route breaks. However, the approach does not provide any hard QoS guarantees or resource reservation mechanisms.
A unified signaling and routing mechanism for QoS support in mobile ad-hoc networks is given by INORA—a QoS support mechanism based one the network layer. It is a routing protocol based solution, which presents an effective coupling between the INSIGNIA in-band signaling mechanism and a temporally ordered routing algorithm (TORA) for mobile ad-hoc networks. The aim is to establish a routing path which is the most suitable to provide QoS requirements for a flow. TORA thereby provides multiple routes between a given source and destination. The INSIGNIA signaling mechanism tries to make soft state reservation along the routing path chosen by TORA. When the current route fails to provide the QoS requirements INSIGNIA interacts with TORA for retrieving alternative routes. Furthermore, INORA makes use of feedback on a per-hop basis to direct the flow along the route-that meets the QoS requirements of the flow. In case admission control fails at an intermediate node, data packets are transmitted as best-effort packets from the source to the destination. The result is that there is no transmission interruption. On the other hand, no QoS guarantees are given.
Information dissemination as described in the article “Information Dissemination in Partitionable Mobile Ad Hoc Networks” (IEEE, October, 1999) by G. Karumanchi et al. is the principle process of replicating information at multiple nodes, and making some data available to a given number of mobile nodes within the network. This mechanism is well suited for spreading some information throughout mobile ad-hoc networks. The author indicates that a hybrid information management strategy and an absolute connectivity-based update trigger policy are particularly suited for partitionable ad-hoc networks.
A further well-known approach is based on the IPv4 Address Resolution Protocol (ARP) as described in the article “An Ethernet Address Resolution Protocol” (RFC-826, November 1982) by D. C. Plummer, which is well established within IPv4 networks. The protocol relies on a broadcast medium, e.g. the Ethernet. Every host has a small cache to save mapping information, and all hosts are synchronized within their status information. Thereby, no distinction is made between clients and servers.
The IPv4 Reverse Address Resolution Protocol (RARP) described in the article “Reverse Address Resolution Protocol” (RFC 903, Stanford University, June 1984) by R. Finlayson, T. Mann, J. Mogul, and M. Theimer also relies on a broadcast medium such as ARP. The difference is that RARP needs one or more server hosts, which respond to RARP requests generated from client hosts to maintain a database of mapping information. RARP is independent of the underlying technology and can be used for mapping hardware addresses to any higher-level protocol address.
The IPv6 Neighbor Discovery Protocol (ND) described in the article “Neighbor Discovery for IP Version 6 (IPv6)” (RFC 2461, December 1998) by T. Narten et al. extends and improves IPv4 ARP. It is embedded within ICMPv6 and defines new functionalities, such as “neighbor unreachability detection”. To perform the neighbor discovery protocol, the node needs to have multicast-capable interface(s). The protocol performs only on addresses that are determined to be on-link; it never performs on multicast addresses. Furthermore, an unsolicited node does not need to create an entry in the cache when receiving a valid neighbor advertisement.
The IPv6 Inverse Neighbor Discovery Protocol (IND) described in the article “Extensions to IPv6 Neighbor Discovery for Inverse Discovery Specification” (RFC3122, June 2001) by A. Conta is the extension to IPv6 ND. It is initially developed for Frame Relay networks, or networks with a similar behavior. Thereby, an ND solicitation is sent as an IPv6 all-node multicast. However, on the data link layer (layer 2), it is sent directly to the target node—a directly connected remote node identified by the known link-layer address.